Originally Posted by
sdsearch
Or at the check-in counter, which has been recommended (in some thread in this forum) in case you don't know how long it will take you to go through security and to the gate, or if it's just convenient because there's no wait when you arrive.
But yes, in any case, it has to be purchased at the airport on your departure day.
If you have a layover, can you upgrade Flight 2 at check in at the airport of Flight 1?